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Dangers to the Engine if CHT goes below minimum in flight during descent?
What are the dangers of CHT going below minimum in flight during descent since the power setting will be around 10inches in a power descent?

This might answer your question https://aviation.stackexchange.com/a/573/33651

To my knowledge, the problem with running low CHT is mainly related to incomplete combustion, leading possibly to fouling of spark plugs and buildup of carbon and lead (if present in fuel) deposits in combustion chamber. How severe this actually is, I have not studied the subject any further, or looked inside an engine during such a condition ;)
However, from experience I can tell that after a prolonged descent, running the engine cool, the engine usually has some "difficulty" picking up the pace as the descent is stopped and power increased. Some sputtering and hesitation are present sometimes, but after a while the situation is normalized. During training, such descents were advised against, and I would say for a reason.
In extreme cases very low CHT might lead to stalling the engine, as it can no longer support combustion due to lack of heat and possibly the fouled spark plugs I mentioned earlier.

It's mostly about the cooling rate.  Lycoming recommends limiting cylinder temperature reductions to less than 50 deg F per minute.  It's especially critical when cylinders are above 400F.  The time when this stress is worst is going from climb power or full power all the way to idle.  Power reductions from cruise, if made gradually, generally won't exceed the cooling rate limit if you take it easy, especially if you have cowl flaps to allow regulation of cooling flow.
Once cylinders have cooled down, structurally there's not a problem; the main problem is just the tendency for plugs to foul after a long run at idle.  Most flight instructors will tell you to give short bursts of power during the descent to help keep plugs clean and make sure the power will be there when you need it.  Also, keep the mixture lean unless you need to go back to climb or max power.
I tend to also bring the power up gently when leveling off because I'm that sort of person, although there isn't really a problem with shock heating, so don't worry about sudden power applications doing damage (still, don't just shove it forward instantly).  Lycoming says if the engine can take full power application without stumbling, it's warm enough.
The cooling rate issues are mostly to do with the different expansion/contraction rates of the materials in the cylinder.  Effectively, the difference in aluminum (head) and bronze (valve guides) contraction rates vs the steel in the valves and valve seats (piston rings too, but the rings are running in a steel barrel so the effect is minimal).
While heating, the non steel parts expand faster than the steel ones; no problem (the interference fit of the valve seat has to account for this so it's still tight in the head when the head is fully expanded).
While cooling however, if the non-steel parts shrink faster than the steel ones, you get potential valve (mostly exhaust) sticking (can become a serious problem because it can bend push rods) and massive hoop stress in the aluminum casting around the valve seat, as the aluminum shrinks faster than the seat.  Cylinders almost always crack between the exhaust valve seat and the spark plug hole, because that little isthmus of aluminum between the two holes is the ideal starter location for a crack.
I have a lot of experience in glider club operations where the engines run full bore, then not, on every flight cycle, and it's murder on cylinders.  Clubs in the 90s started to use special power reduction protocols to keep the cylinder cooling rates in limits after glider release, and this drastically reduced the incidence of cracked cylinder heads.  This is a big deal going from full throttle to idle; going from cruise power with a lower cylinder temp is not so bad. It was found from the glider club research that once the cylinder head was down to the low 300s F, high cooling rates below that had no significant effect.
So, in general, if you just take it easy on the poor old engine, by reducing power gently at first until the cylinder temps have dropped somewhat, it'll be ok.

Manifold pressure in the descent isn't the issue; maintaining an adequate cylinder head temperature, and reducing the rate of CHT change is the issue.
Keep in mind what manifold pressure is: it's a measure of vacuum, or the lack of it. It's a measure of pressure in the intake manifold.  There are a lot of myths floating around about manifold pressure, ranging from the notion that manifold pressure and engine RPM must be be the same or never "oversquare" (very untrue), to my favorite, an engine failure leads to zero manifold pressure (was actually told that by a F22 pilot after he had a power loss in a recip powered airplane--confirmation bias).
Think of the manifold as the hose on a vacuum cleaner.  Shut off the vacuum cleaner (shut off the aircraft engine), and the manifold pressure will be barometric pressure, regardless of throttle position (so, 29.92" hg or 1013 mb on a standard day at sea level).  Start the engine (start the vacuum cleaner), and close the throttle, and the manifold pressure goes down, because the vacuum (engine) is drawing air from the manifold...if the throttle is closed, it's reduced the amount of airflow through the manifold, so if the engine (vacuum cleaner) is drawing more air than flows through the throttle plate, the manifold shows lower than barometric pressure.  That's all it is.  The throttle is an airflow valve, and the engine a suction machine.
As a result, for 10" of manifold pressure, one can't say that CHT is low due to manifold pressure low.  One needs to look at mixture, cowl flap setting, and airspeed, and other factors, to determine what cylinder head temperature (CHT) will be.
As a general rule, it's not good practice to make idle descents in piston engine airplanes.  The common guidance is to keep the power setting "at the bottom of the green," which in most airplanes is about 15" hg.  That's generic guidance, with the intent of not only giving enough power to keep the engine warm, but to reduce the propeller driving the engine.  It's best if the propeller is producing thrust, or close to zero thrust, but not less than that.
High temperature is a bigger problem.  The interface between the steel cylinder barrel and the aluminum cylinder head is what keeps the cylinder head in place.  If that head gets too hot, burning valves or warping aren't the only dangers.  Lifting a cylinder head, or in other words, separating the cylinder head from the barrel, is a danger.  The cylinder head is fit to the cylinder barrel with an interference fit and some slight features on the barrel that help prevent the head from coming off.  Mostly, however, it's just a tight fit.  Get the cylinder head hot, let it expand, especially if it expands too rapidly (gets heated too rapidly), and the head can separate from the barrel under pressure from the combustion chamber.  This invariably results in additional damage and possibly a fire.
Piston engines should be warmed up gradually and cooled gradually; there are aluminum parts, and steel parts which warm and cool at different rates.  Aircraft engines are quite tolerant of a wide range of temperatures, and even the effects of air cooling (and cooling from rain and precipitation), but it's best to respect the engine and not abuse it.  Consistent operation, and operation at enough power to seal the rings and prevent blow-by, at mixture settings adequate to prevent detonation (not usually a factor below 75% power for a given engine), and of course regular operation within the engine operating limitations, will go a long way toward helping ensure long engine life.
There is both anecdotal, and actual evidence of cylinder head cracking or "shock cooling" from rapid cooling of cylinder heads.  I've changed enough of them personally, with cracks in the head, often between the spark plug holes, but also between fins trending toward the barrel interface, to offer anecdotal experiences.  It's also accounted in various manufacturer information stretching back before the second world war.  That said, there's also a lot of myth surrounding "shock cooling," and some strong arguments made that it's more myth than reality.  My preference is to not abuse engines, and that's especially true of high performance engines, geared engines, turbocharged, supercharged, or turbosupercharged engines which can experience some significant temperature ranges and some high power settings (and potential for detonation, another subject).  Carry some power in the descent: it's not a turbine engine.  If you have cowl flaps, watch the temps, work the engine, airspeed, and cowl flap setting accordingly, and if needed, start your descent a little earlier, with a little more power.  Problem solved.


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Is there a legal minimum stop time between 2 legs?
This question is restricted to airliners transporting many passengers (let's say more than 20).
Between two legs, airliners stay at the boarding gate for a limited time, sometimes less than an hour. The stopover duration at the gate is typically dictated by the time to refuel and disembark/embark both freight and passengers. I understand the cost-saving logic behind the decision to make this operation as fast as possible.
However, in a competitive market, safety may not be compatible with shorter turnaround times. No pilot would irresponsibly compromise safety by leaving the gate without fulfilling their safety and security obligations, but I wonder if there is a minimum turnaround time imposed by regulation to avoid downward pressure on turnaround times?
EDIT:

let's focus on the fastest and simplest scenario: no crew change and no refueling (the crew took enough fuel to make several legs)
I don't want to be restricted to one legislation or one part of the world. The question is: does any regulation exist to require such a stop time?
I just thought that technically, brakes should be cooled down before the next take off roll.

The limiting factor in plane turn around time is in normal situations, the speed of passengers being unloaded, and new passengers loading onto the plane.   Ryanair have this down to a fine art, and do run schedules where planes have 20 minutes between the landing and take off times.

Legal questions should be limited to one set of rules/laws so that an accurate answer can be provided. Unless someone is familiar with the aviation laws of every individual country in the world, this question is impossible to answer as written.

@Lnafziger Well, impossible to answer in the negative anyway.

No, there is no legal minimum turnaround time.
There are several technical reasons why an aircraft needs to stay on the ground for a while. Some of the (already mentioned) time consuming tasks are:
Passenger (de)boarding, crew change, refueling, brake cooling, obtaining ATC clearance, visual inspection of the plane etc.

You could also add engine cooling to your list. I recently flew on an intra-island flight on a BN Islander. Talking to the ground staff, they mentioned the airport was capable of taking larger aircraft (such as the Twin Otter), however it didn't fit their ops model - it needed a lengthy delay before restarting the engine again.

Generally, AFM limitations are legally required to be complied with...

Well, in some cases, zero.
In Australia, for a long time only two airlines (Ansett and TAA) were allowed to fly between capital cities. To work around this, East-West Airlines practiced a touch-and-go at Albury, half way between Melbourne and Sydney. Legally, these we considered separate legs (at least for some time).

Wow, that's crazy! Thanks for the history lesson :)

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Why is Airbus proceeding with both the A330neo and A350 XWB?
Looking at the specifications for the A330neo and A350 XWB, it strikes me that the two under-development models of the A330neo are relatively similar in specification to the A350-800, one slightly shorter and one slightly longer, with corresponding variances in passenger numbers. List pricing (for what little it's worth) is approximately the same, as well.
As a result, it seems like having two distinct models competing for essentially the same market segment should just increase costs for Airbus, and it's not clear to me what the gains are. Is it easier to sell the A330neo to airlines because of it's relative similarity with the existing A330? Is the A330neo cheaper to operate than the A350 (this seems dubious given cost of operation is one of the big selling points of the A350)?
There's been some rumours about the A350-800 getting cancelled and customers pushed towards A330neo or larger A350 models; this still counterintuitive to me. Surely having a smaller range of aircraft families (i.e., A320, A350, A380) simplifies a lot (manufacturing, certification, etc.), so why increase the number of families instead of a smaller A350 model?

Mainly because of customer concerns.
Airbus, or any other aircraft manufacturer can propose a bunch of variants in its catalog, but it's the airlines that defines what aircraft are to be developed next. (On a timeline of 10 years up to 30 years - I don't recall the link, but that's Lufthansa Group's explanation.)
Since the decline of the A340s and 747s, and the success of A330s and 777s (mainly fuel saving and engine maintenance), airlines were in a rush to go twin engined while avoiding mass qualification trainings for a new type as long as possible (A350 and 787). Replacing type for the latest generation counterpart is relevant when a) investment is less than predicted gain, and b) the new type matches traveling volume.
The deal is to attract as much customers as possible from a manufacturer's point of view. The way it is now, you can expect Airbus beating Boeing at that game of both new types and neo ones as a kind of revenge over the 777 beating the A340. The only market where Boeing is still strong is on aircraft the size of the 767-300ER, and therefore doesn't need a re-engined neo-like, nor a new type, as long as no other manufacturer is capable of building a next gen version on that market. On any other Boeing vs. Airbus market, they are roughly on a draw (737s vs A320s, 777s vs A330s).

People like to say that the 787 is the successor of the 767. That can be true between the 767-300ER/400ER and a lightweight version of the 787-8, but the comparison stops there, and the 787-9 is likely to get more orders than -8 anyway. In terms of size, the 767-300ER/400ER and 787-8 are very similar. But when you have a look over payload, range, cabin width and fuel consumption, there's a huge gap, and that's what matters for airlines, not size or overall shape. Remember, the 777 was also supposed to be the successor of the 767, but ended on a completely different market.
In fact, because Boeing already has the 777-200ER/LR, it doesn't make sense to launch a successor while the 777 is still strong. That's also why the future 777-X are larger, to make room for the 787-9 and -10, and also why the -10 is supposed to be launched as late as possible.
Airbus, on the other hand, had to drop the A340 program earlier than expected, despite the launching of the -500 and -600 versions. A330s cannot be upgraded like the A340 without heavy structural changes, that's where the A350 enters the stage, and why the A330 is still a good candidate at being re-engined and improved in terms of payload and range. We can say that Airbus were always late to take the lead over Boeing, but that's the result of being as diverse as the countries involved, and the absolute need of a success in bringing the first full length double-decker widebody airliner.
Boeing also made some weird decisions, like the 747-8I (not the freighter), the 767-400ER and the 787-3 (now cancelled). The 747-8I were supposed to seduce Chinese market, and airlines that were historical customers of the 747 production line. But by the time the 747-8I entered service, twin engined long range airliners already took the lead, were proven more fuel efficient, cheaper in maintenance costs and much more versatile, which match with Boeing philosophy towards the point-to-point theory. Filling the gap between the 777-300ER and the A380 wasn't that good of a move. The 767-400ER was neither much more profitable than the 767-300ER, nor the 777-200ER on their respective routes. The 787-3 obviously aimed the Japanese market (and Chinese domestic routes) where 737s/A320s and 767s were still going well. Initially postponed after 787-9 development, it was finally cancelled. Actually, the current Airbus position about the A350 -800 is quite the same as Boeing's back then with the 787-3. Difference is, the A350-800 is larger than the 787-3, and is the direct competitor of the 787-8 and -9, and depending on travel trends, probably a strong opponent to the 767-300ER.
Knowing all that, Airbus wouldn't risk shorter or longer versions of the A330, and opted both for one type that can be stretched (A350) to fill the void created by the demise of the A340, and current A330 by increasing the operational service lifetime with the neo version. Next is up to travel trends, which is the most difficult part to estimate...
Having the latest iPlane is seducing, but not everyone can afford it.

Good discussion, one other factor may be having multiple production lines. Two similar aircraft may not make sense on the same production line, but if you need two or three production lines like in Asia, Europe, US then it may make sense to have some variance between them.

Actually the A330neo is already eating up into the A350-800 orders so much that they have abandoned it.

“Their A350 strategy has failed -- they’re really down to one successful model,” Boeing Marketing Vice President Randy Tinseth told reporters at the Farnborough expo near London. “If they didn’t make this choice, they’d be headed for a 30 to 35 percent share in the 200- to 400-seat market.”
Customer feedback about the A350-800 spurred Airbus’s decision to abandon the plane, said Fabrice Bregier, who leads the airliner unit at the Toulouse, France-based company. Stopping work on that jet will let Airbus focus on the more successful and larger -900 model and respond to some airlines’ concerns for fixes to the biggest version, the -1000.

Hmm, the Airbus website still lists the A350-800. It sounds like there was an expectation it was going to be dropped, but it's not actually happened yet? Still, if it is dropped, let me change my question to "why introduce another model instead of a shrink of an existing one"?

@gsnedders The orderbook is 16, which I doubt is something Airbus will go forward with. My guess would be that Airbus is negotiating with the airlines to switch to other aircraft. Actually, 350-800 is a new aircraft, while the 330neo is basically a reengined variant with some improvements.

@aerolias: that is what the Wikipedia article says, quoting the AIrbus chairman over a year ago - Airbus have been encouraging airlines with A350-800 orders to switch to either the A350-900 or the A330-800neo. Then Airbus only need two A350 variants to meet airline demand.

As the years go by more people travel which means bigger aircraft are
required. The a350-800 is too small and yes it will probably be
canceled. Airbus has a lot of customers for the a330 and they want to
sell more and if they make the a330 more efficient then the more
customers want this aircraft. Thats why the 737MAX,a320NEO,
a330NEO, E-(75,90,95) e-2,( and 777x are in development
because of the amount of customers that aircraft has and more
costumers are going to want the more efficient version.
The a330NEO design is to directly compete with the 787 and the 767  The a350 design is against the 777 and so their goal is to improve thrust and efficiency over the 777 with the new a350.
Thats why they designed both
aircraft (a330NEO, a350). Its pricey, but they make a lot of money
designing both of the aircraft. The a330 is already a very popular
aircraft and making a version that is more efficient will draw in
more customers. So in conclusion you can sell many different families
of aircraft that are popular and increasing efficiency in the
aircraft will draw in more customers, although it would be very
pricey Airbus would still make a lot of money from both the a330NEO
and the a350.

I think you've oversimplified the situation, and flipped some of the details around. A330 competes primarily against 767 and 787, while the A350 is larger and more realistically compares to the 777.

@egid Okay I will edit it.

"More people traveling = bigger aircraft needed" was Airbus' theory behind the A380. Based on sales of the A380, and the 747, looks like that theory is wrong. At least for now.

Well, I think the A380 was the result of a good idea taken too far. The airline industry is modernizing and "rightsizing" with the next generation of planes, balancing airport congestion with a general decline in passengers due to communications technology and economic concerns. The result is a focus on two aircraft classes; the "mid-body" (B737, A319/320/321) and the "widebody" (A330, 777/787). The mid-bodies are being "stretched" as weight and fuel efficiency improve, while the widebodies are focusing on efficiency so it's practical to use them instead of jumbos despite reduced capacity.

In both cases, you can move more people with fewer planes, without going to the extreme of a four-engine like the 747 or A380, which pretty much has to be full to be profitable.

@KeithS In about 10-20 years or so the demand for an aircraft like an a380 or 747 will be much higher. Back in the 20th century the demand for smaller aircraft was high. Now the demand is for wide bodies. In 15 years the demand could be for jumbo jets.

@Ethan - That's pure speculation. EADS/Airbus began A380 design development in 1988, two decades after Boeing proved that the gamble of a very large aircraft could work (and it was a gamble; Boeing went $2 billion in debt on the 747 project during preproduction). However, the 747 was successful in a highly regulated market prior to the information age, when there was significant demand for VLAs on well-travelled routes. The A380's first flight didn't occur until 2005, 4 years after 9/11 and over 30 years into deregulation, where VLAs only make financial sense for ultra-long-hauls.

See my answer to a related question about why the A380 hasn't done well in general: http://aviation.stackexchange.com/questions/17374/why-couldnt-the-a380-secure-any-orders-for-two-straight-years/17392#17392 In short, the A380 is the most expensive airliner ever, it entered a fairly saturated market (its saving grace was Emirates' development into a ULH airline), it had significant "teething" issues that scared away orders, and it forced airports to redesign their VLA jetways to accomodate it, while Boeing's 747 was a known quantity and its newer widebodies are close in size to the 757/767.

Simple math : you can trade one A380 for two A330, and have roughly the same operation result (no airline uses max seating config) That also means that you can either have two flights a day instead of one to the same destination, or one more destination on your routemap... The question is, are there more passengers buying tickets to board on the biggest flying toy on earth, or more passengers that only want to reach their destination each day...

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How could MH370 fly west when satellite pings went east?
I have a question perhaps best demonstrated with this image:

Malaysia published two maps with the preliminary accident report which allege MH370 flew west from Penang to MEKAR (above Aceh Province) and then between 18:25 UTC and 19:41 UTC flew west into the Indian Ocean.
The problem is the Burst Offset Frequency chart published 24 March shows a frequency drop after 18:25 UTC signifying flight away from the satellite.
After MH370 allegedly emerged from the Straits and turned south the track which Malaysia's Preliminary Accident Report claims MH370 flew (based on their analysis of the BOF chart data) the track makes even less sense because the distances away from the satellite continue to increase.

And this image shows the distance relationship with the satellite:

There are also other (non satellite) reasons to question the validity of the alleged track through the Straits of Malacca. First is the claim MH370 was seen flying west by radar at Surat Thani in Thailand. That radar has a published maximum range of 200nm. Kota Bharu is 240nm away from Surat Thani.

This is not the only reason to doubt the alleged MH370 flight though the Straits. Malaysia presented this image to Chinese relatives at the Lido hotel in Beijing on 21 March and told them it was a military radar image from Butterworth of MH370 in the Straits of Malacca. They said it crossed the island of Pelau Perak at 18:02 UTC and disappeared at 18:22 UTC.

The image however omits other aircraft known to be present at the same time:

Worst inconsistency of all however is this, the radar image does not even come from the Butterworth radar. The real military radar used by Butterworth is a Thales Raytheon GM400 which has a screen display like this:

I don't understand how so many supposedly intelligent "experts" and journalists have managed to be deceived for so long except to say people believe only what they want to believe and shut their eyes to the truth.
Australian, Malaysian, Japanese, New Zealand and Chinese taxpayers collectively forked out $90m wasted taxpayer dollars for a search at the end of this projected BOF track in April which turned up no result.
My question is how does this mutually incompatible information prove MH370 flew west through the Straits at all?

Could you possibly include the position of the satellite at 18:25 as well as the angle that it was pointed at.  It's hard to understand what you mean without knowing the location of the satellite and the angle it was at when the data was gathered.

Jay the satellite distances actually reduce by 5 nautical miles yet the BOF chart has the satellite receding away at speed.

Articuno it is incompatible for the satellite handshakes to be moving apart when investigators claim MH370 was flying towards the satellite. I can't explain it any clearer than that.

@Articuno: The vertical axis is Doppler shift, which is proportional to speed relative to the satellite. The satellite should be Inmarsat-3 F1 geostationary at 64.5° E, 0° N.

@Articuno: They correspond to changes of velocity component toward the satellite. In the area of question it may mean change of speed when flying east or west, but has to mean change of direction when flying north or south. It may also mean a change in altitude, because the satellite is much more above than west of the point (geostationary orbit is ~36 thousand km, or over 19 thousand nautical miles, above Earth)

Your maps are not oriented with North at top, you don't mention map projection, you don't seem to be using spherical trigonometry and you don't seem to take into account satellite altitude and motion. Can you provide details of the mathematical model you are using which gives results differing from the tracks published by the Malaysian Ministry of Transport?

@Articuno asks "Why couldn't the pings be getting farther from the satellite and MH370 be moving westward?"because the satellite's location is east of India. The image is taken from the satellite's vantage. For the period after 18:25UTC the BOF chart shows dramatic frequency reduction which equates to velocity away from INMARSAT. The track proposed by Malaysian investigators claims it flew west towards INMARSAT at this time. It is impossible for both claims to be true.

@Articuno asks: "So deviations up and down in the vertical axis correspond to velocity changes, and not necessarily a change from westbound to eastbound or vice-versa?" No the increase in frequency relates to signal compression caused by the doppler effect. Doppler compression can only occur if there is a net velocity towards the satellite and that equates to a flight in a net direction west, yet after take off the BOF chart shows frequency increase whilst radar tracked MH370 flying away from INMARSAT... It is fundementally wrong. It is not about the semantics of inclination angles.


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How could MH370 fly west to Straits of Malacca within time frame without being seen on Radar?
Malaysia originally claimed they saw MH370 on military radar climb to 45,000ft (in excess of its service ceiling) then drop 40,000ft (12,000m/6.47nm) within 60 seconds.
Prior to May 2014 Malaysia claimed MH370 was seen on radar flying IGARI-VAMPI-GIVAL-IGREX, but when asked to produce radar tracking data for this could not do so.
In the Preliminary Accident Report published 1st May 2014, the report stated unequivocally that it was not seen on LUMPUR civil SSR radar after 1:21am until next seen in the Straits of Malacca on military radar. Malaysia could not or would not publish radar imagery for the mystery aircraft sighted in the Straights of Malacca, however on 21 March they displayed this image at the Lido Hotel in Beijing which they claimed showed MH370 in the Straits of Malacca:

By default therefore this image has become the de facto radar image for MH370's flight which incidentally does not show MH370 flying IGARI-VAMPI-GIVAL-IGREX.
This is part of that image with time stamps made clearer by focus sharpening tools:

Using the time stamp imagery it is now possible to calibrate that flight more precisely by measuring the time elapsed over known geographical points and then creating a calibration scale beside the track.
That calibration suggests that this aircraft flew over a small island, Pelau Perak at precisely 2:03am on a track leading back to the southwest tip of Palau Penang.

The preliminary accident report also notes MH370 was reported by Ho Chi Minh being lost over waypoint BITOD at a time which is inferred as 1:24am MYT. The Preliminary Accident Report issued by the Malaysian Government states unequivocally that it was lost from radar at BITOD.

This poses a serious problem since it appears to only allow MH370 39 minutes to return to Pelau Perak at the maximum speeds for low altitude flight.
This flight over a track distance of 338nm requires an average TAS airspeed of 520kt. Something which requires the aircraft to fly at altitudes where it would logically have to have been seen by several radar stations. Radar at Aceh and at Singapore must have seen MH370 flying west flying at 38,000ft yet they did not.
If MH370 flew west at these altitudes it should have been seen by at least half a dozen radar stations. Malaysia however claimed that it flew back at 5,000ft like a fighter plane to evade radar and flew low over Kota Bharu. How could it do all this if it had to maintain a speed only achievable at 38,000ft?

The air temperature at Kota Bharu was 22 deg C and there was a light nor-easterly breeze of between 5-10 knots.
VMO for a B777 with this surface temperature is 350 knots TAS at 5,000ft. At this altitude logically it could not have flown west within 39 minutes. Even if one is generous and allows that it turned back at IGARI affording another three minutes it still does not seem credible since the track would still require 54 minutes of flying.

So the question is how did this aircraft fly back west so fast without being seen?
Did it fly low, or did it fly high?
The captain of JAL750 reported he spoke with the co-pilot of MH370 by VHF just after 1:30am. He said all appeared normal when he spoke to MH370. JAL750 at that time was flying NE from Ho Chi Minh at 32,000ft.
JAL750 was at least 398nm away from IGARI. Had MH370 dropped to 5000ft and flown west it would have been out of VHF range to speak with JAL750. This image has a circle for the estimated radar horizon between JAL750 and another aircraft at 5,000ft.

I would appreciate if I someone could give a cohesive explanation for apparent inconsistencies in the official account?

It never got to BITOD, you have to remove a bunch of miles from your computation
your times are off, it was at MEKAR at 18:22, giving 19 extra minutes w.r.t. what you claim

@Federico the question is not how it made it to MEKAR. The question is how it made it to Pelau Perak in just 39 minutes? Malaysian claims Radar images show it over Pelau Perak at a precise time and that time defies the laws of physics. Ho Chi Minh contacted Lumpur control at 1:38am and said they lost MH370 off their radar at BITOD and this is in the official Preliminary Accident Report. MH370 also spoke to JAL750 which was over Vietnam after 1:30am by VHF. JAL750 could not communicate with MH370 by VHF if it was flying west from IGARI at 1:30am because of the earth's curvature.

@user2357: I think you may misunderstand this website. It's where current and former private and commercial pilots and aviation enthusiasts ask and answer questions about aviation (not about the competence or veracity of government officials). It's not necessary to be a genius to participate here. Just to have a question about aviation or be able to answer questions about aviation.

How can you calculate the required TAS if you don't know the wind speed? How can you calculate the maximum TAS if don't know temperature? Where does your claim "38,000ft or above" come from? (hint, it's false) How do you know it would have been seen by half a dozen radar if you don't know what the atmospheric propagation was, nor whether those radars were operated at full power or at all at the time? One more observation: flying faster than Vmo is not busting a law of physics, merely busting a legal law. I doubt though whether the aircraft was in fact at 5000ft, likely much higher.

@  DeltaLima the windspeed was below 10kt breeze from the north east and air temperature at Kota Bharu at 2am MYT was 22 deg C. I factored the air temperature in before calculating the TAS

@user2357 Regarding your speed calculations, remember that while waypoints are fixed by the earth's surface aircraft aren't: A 10 knot breeze & warm temperature on the ground means nothing to an aircraft up in the flight levels. For example: right now the surface winds at JFK are around 12 knots and it's 24 degrees C. At 35,000 feet above the same station the winds are forecast at 71 knots, and the temperature around -37 degrees C. Thus to calculate expected travel time between waypoints you need ground speed (derived from True Airspeed and Winds Aloft information from the incident date).

The essence of your question seems to be
Did Malaysian officials claim MH370 flew from BITOD to Palau Perak in 39 minutes?
Currently I don't see enough primary evidence to support that claim.

Use of waypoint names by officials
It is clear (to me at least) that when officials talk to the press, they use waypoint names rather than baffling the journalists by reading out lengthy sets of latitudes and longitudes. Waypoint names are less likely to be confused or mistranscribed than lengthy sets of digits. It is also likely that as the information passes from technical staff examining logs up to officials, that indigestible coordinates are simplified to waypoint names to help those officials quickly grasp the essentials. I believe it is a mistake to infer any specific accuracy such as *within 1 nm of the named waypoint", It is probably best to interpret any mention of a waypoint as meaning the aircraft was closer to this waypoint than to any other major waypoint.
When an official reports that MH370 flew on a route between IGARI and VAMPI, I believe it is a mistake to infer that they mean the aircraft flew from a position precisely at IGARI along a "straight line" to a position precisely over VAMPI. I would infer no more than the aircraft spent some time in a large area bounded on the east by IGARI and bounded on the west by VAMPI and that it was headed in a direction that took it more towards VAMPI than IGARI. It might have flown roughly SW or roughly W or any direction in between.
The evidence that MH370 was in the region of BITOD is in this document

Again, I would interpret that generously. It doesn't mean that MH370 was within some immeasurably tiny distance from BITOD.
There is of course also the possibility that the "radar blip" was a flock of birds.
Times
I note that there is no mention in the document above of HCM's record of the time the "radar blip" was somewhere closer to BITOD than to IGARI.
You say "at a time which is inferred as 1:24am MYT." but you don't say who made that inference and you don't provide any references to official information. The question would, in my view, be a lot better if it gave references (links) to official Malaysian documents for each claim made.
Since the question doesn't show that the Malaysian government stated that they believe MH370 was at BITOD at 1:24am MYT, it isn't possible to identify any inconsistency.
Palau Perak
On the very heavily annotated images you show, it looks like the label "Palau Perak" was added by some anonymous person and was not present on the original slide shown at the press conference.
To draw firm conclusions, I believe, you really need to make use of more direct and clear information.

Conclusion
At the moment, I don't think there's sufficient primary evidence to identify any incontrovertible inconsistency. I look forward to seeing some better references edited into the question.

Infact there is no primary evidence that it ever flew back from either IGARI or BITOD. If you insist on primary evidence then where is the radar evidence that it flew west at all? Indonesian military radar at Aceh saw no aircraft fly the route alleged by Malaysia. In fact two aircraft known to be in the same vicinity at the same time SIA68 and EK343 are not even present in the Butterworth radar imagery so Perhaps I should ask you for verification that there is any primary proof at all of any aircraft flying Penang-VAMPI-MEKAR?

@user2357: My answer stands: No, Malaysion MOT didn't make the specific claim you ascribe to them. If you'd like to ask a separate question about aviation, please do - but it might be better in Skeptics if you can identify a specific claim clearly made by Malaysian MOT of which you are skeptical.


text:
Are you required to record flight hours of serialized parts?
Is it a requirement to record/maintain flight hours for serialized A/C parts? I have searched the FAA website with no luck.

For the airframe, engine yes, but I don't believe you have to break it down by component. What parts are you talking about in particular?

Short answer: only for the airframe, engines, propellors and rotors (as applicable).
This legal interpretation is a response to someone who asked which records are required to identify when life-limited parts need to be replaced. It says that you're only required to keep flight time records of the airframe, engine(s), propellor(s) and rotor(s), as appropriate:

Existing regulations, specifically 14 C.F.R. § 91.417(a)(2)(i), require
  each owner or operator to keep records containing the total time in
  service of the airframe, each engine, each propeller, and each rotor.
  This is accomplished by the owner or operator recording and tracking
  in some form and manner the time in service of the airframe,
  engines(s), propeller(s), and rotor(s) from the moment the aircraft
  leaves the surface of the earth until it touches it at the next point
  of landing, as referenced in 14 C.F.R. § 1.1. In addition, §
  91.417(a)(2)(ii), and similar provisions in 14 C.F.R. §§ 121.380(a)(2)(iii) and 135.439(a)(2)(ii), require owners or operators (certificate holders) to keep records that show the current status of
  life-limited parts of each airframe, engine, propeller, rotor, and
  appliance.

91.417 does indeed say - among other things - that owners and operators have to record the time in service and status for the airframe, engines, props and rotors, but only the status for life-limited "appliances":

(2) Records containing the following information:
(i) The total time in service of the airframe, each engine, each
  propeller, and each rotor.
(ii) The current status of life-limited parts of each airframe,
  engine, propeller, rotor, and appliance.

1.1. defines "time in service":

Time in service, with respect to maintenance time records, means the
  time from the moment an aircraft leaves the surface of the earth until
  it touches it at the next point of landing.

And 43.10 defines "life-limited parts":

Life-limited part means any part for which a mandatory replacement
  limit is specified in the type design, the Instructions for Continued
  Airworthiness, or the maintenance manual.

To summarize:

You only need to record service time for the airframe, engine, props and rotors
For any other life-limited parts, you only need to record their status, i.e. you need to be able to say when it's time to replace them

Things get a little more complicated with life-limited parts if the part is intended to be reused (transplanted from one airframe to another, like if you wreck the wing on a Tomahawk and replace it with one from a salvage yard). Most folks I know interpret 43.10(c) as "Write the accumulated hours/cycles on the yellow tag when you pull a life-limited part." because otherwise you wouldn't be able to determine the status in a new installation.

14 CFR 91.417(a)(2) States:

(2) Records containing the following information:
  (i) The total time in service of the airframe, each engine, each propeller, and each rotor.
  (ii) The current status of life-limited parts of each airframe, engine, propeller, rotor, and appliance.
  (iii) The time since last overhaul of all items installed on the aircraft which are required to be overhauled on a specified time basis.
  (iv) The current inspection status of the aircraft, including the time since the last inspection required by the inspection program under which the aircraft and its appliances are maintained.
  (v) The current status of applicable airworthiness directives (AD) and safety directives including, for each, the method of compliance, the AD or safety directive number and revision date. If the AD or safety directive involves recurring action, the time and date when the next action is required.
  (vi) Copies of the forms prescribed by§ 43.9(d) of this chapter for each major alteration to the airframe and currently installed engines, rotors, propellers, and appliances.

In addition, if you read closely (a)(2)(ii) requires you to keep records of any life limited parts which means that if the manufacturer identifies it to be "life-limited", like a gearbox, then the status for that must be recorded as well, with some exceptions for the time being included in other life-limited recordings.
How do you know if it is life-limited? You need to read the Type Certificate Data Sheet, Airworthiness Directives, or Limitations of FAA approved manuals. Its also useful to note that while you certainly can keep copies of records in computerized form, the FAA requires paper records mostly because there is a signature requirement that is not satisfied by electronic signatures.


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How strong is the A380 fuselage-wing joint?
The Airbus A380 has a maximum take-off weight of almost 600 tons. How strong does the joint between the wings and the fuselage have to be so it doesn't break? And how could it be trusted unless real-time fractures don't occur? How was it tested? I mean, you cannot accomodate such a big joint in a wind tunnel except in computer simulations.

Hello! Your question is a bit "open-ended". On "how strong ...", the only possible answer is "very strong", which isn't exactly helpful. Maybe you want to ask for instance how is the necessary strength measured, or how is the joint tested for being compliant with the requirements?

As stated in one of the answers, a typical test stress in mechanical engineering is 1.5 times the rated load. There is a whole body of experience in materials science, metallurgy and non-destructive tests (radiography, ultrasound, fluorescent dye penetrant, magnetic and eddy current, etc.) that is relevant to mechanical engineering in general (and by extension, to the mechanical branch of aeronautical engineering.) The types of tests done depend at least as much on the material used as they do on the application. Inspection scheduling is obviously particularly important with aircraft.

@steveverrill Please post answers as answers, not comments.

A significant point missed by the question is that the wings themselves weigh about 30t each, empty, and hold the majority of the 260 tons of fuel loaded into the plane at MTOW. So, of the 600t, around half is actually in the wings so doesn't need to be supported by the wing joints because it's the wings that are generating the lift.

@DavidRicherby Yes,that is definitely true !!

The details of the strength required are likely to be complicated and proprietary. However, we can do a very rough estimate.
Using the equation for estimating root bending moment here, and the following numbers:

Fuselage weight: 230,000 kg

MTOW: 577,000 kg
Engines: 25,000 kg
Fuel: 260,000 kg
Wings: 60,000 kg

Wingspan: 79.75 m
Wing taper ratio: 0.17

The equation gives a root bending moment of 17,300,000 Nm. Of course, this is just a static load. If you consider a 2.5 g pullup, this could be 43,300,000 Nm. But on the ground, the wings will bend under their own weight. Running the bending equation on the wing weight, and adding in the engines, gives 23,900,000 Nm in the other direction.
As to how it can be trusted: a lot of math. Organizations like EASA expect way more accuracy than my above estimate, which requires analysis of the specific loading conditions that need to be met, both static and dynamic, and the specific design of the wing, structurally and aerodynamically, which is how aerospace engineers earn the big bucks.
Of course the A380 is bigger than anything mass-produced before. But the in-depth analysis will take this into account. Airbus has some experience building large aircraft, so they have a pretty good idea of what works and what doesn't. Detailed testing is also done, on everything from the nuts and bolts up to entire airframes. All of this information is used to back up the design. Airbus isn't going to invest money in a large test without being reasonably sure it will work, and EASA isn't going to certify a design until it has been successfully tested. Modern analysis allows predicting pretty accurately where and at what load structure will fail.
But even then, with something so large and complex, things happen. Important things like the wings are required to not fail even if they are damaged, and to have redundant load paths so that even if a part fails, the remaining structure will hold. Parts are inspected to look for damage before it becomes critical. Problems are found. More analysis is done, and fixes are implemented. Usually this won't be an issue of "the wing can't handle the load", but that "the wing wears out too quickly". Fatigue is harder to predict and design for.
The FAA requirements are in 14 CFR Part 25. This includes:

Unless otherwise specified, a factor of safety of 1.5 must be applied to the prescribed limit load which are considered external loads on the structure.

So they must take the maximum load expected without permanent deformation (limit load), and allow a 1.5 safety factor on top of that without failing (ultimate load). In order to show that the structure is capable of meeting the requirements:

Compliance with the strength and deformation requirements of this subpart must be shown for each critical loading condition. Structural analysis may be used only if the structure conforms to that for which experience has shown this method to be reliable. The Administrator may require ultimate load tests in cases where limit load tests may be inadequate.

This means that all analysis has to be shown to be reliable. This must either be tested, or compared to the known performance of previous designs. The testing must also be sufficient to prove the requirements will be met.

how could it be trusted?

Like all aircraft, type certification requires that these be tested. I think the wings are tested to 1.5 x their load limit.
A380: STRUCTURAL STATIC TESTS

The A380’s structural static tests on began in November 2004, in preparation for the first flight clearance.
The tests included: Flight Test Installation (FTI) calibration test, maximum wing bending at limit load, ailerons and spoilers functioning test during max wing bend, fuselage pressure test, and fatigue tests and flight cycles simulation.

They place an airframe into a test rig and increase the load on the wings until the wings break. The empirical evidence is compared with the predictions made by mathematical models.

Airbus A380 wing test

Airbus A350 wing test ... (A350 torture video)

Boeing 787 wing test

This.  Engineers don't leave things to chance and models - models help design, but they test exactly how something will break by actually breaking it, just to be sure (and to help make the next models better).

The ugly truth is: Cracks do occur, and have occurred on the A380 wing root, but that is normal. Read on for more.
The static load is only one aspect. Normally, what is driving the design is the fatigue load, which is the constant jerking of aerodynamic and inertial forces on all parts of an airplane. Today, aircraft are designed such that cracks will not become threatening between two inspection intervals.
This technique was learnt the hard way with the aircraft of the late Forties and early Fifties. Up until then, the operational life of metal aircraft was in the order of tens of hours. Parts were designed for the maximum static load plus a safety factor of 1.5 to 2.0. Fatigue was not considered.
Wooden aircraft have no fatigue problems, however, aluminum is extremely sensitive to cyclic loading. Cracks will appear after enough load cycles even at very low stress levels, and will grow with any additional load cycle. Now the approach is to define inspection intervals such that cracks which start right after the last inspection will not grow to a point which threatens structural integrity before the next inspection is scheduled. To ensure this, all major parts need to be made of two load-carrying members, one of which could fail without causing the whole part to fail.
Now we have established that each part of the fuselage-wing joint is made of two parallel members, each of which is able to carry the full limit load for which the part has to be designed. We also know that this strength can only be guaranteed for a part of the aircraft's life. In case of the A380, two things combine to make the wing root design a particular challenge. The first is scaling laws: If something grows in size, its volume and mass will grow with the cube of the size increase, but the cross section of the load-carrying structure will only grow with the square of the increase. The second factor is the high cruise Mach number of 0.85 of the A380. This had been demanded to make sure that flights with the A380 will not take more time than flights with any competing airliner, so that A380 flights are always on the first screen of the booking systems.
The high cruise Mach number demands a thin wing airfoil, and the scaling laws mean that an A380 will need relatively thicker flanges and fittings than a smaller aircraft. This can be computed with high accuracy with finite element codes like Patran in combination with NASTRAN, or ANSYS. After the computational design, one wing has to be loaded until it breaks in a test rig, and another wing will be subjected to simulated flight stresses in another test rig. Here the gust loading is important, which cannot be simulated in a wind tunnel. Therefore, the wing is loaded by an array of hydraulic jacks which are computer-controlled to simulate aerodynamic loads. When enough testing has been done, the aircraft will be certified for an initial number of flight hours which will be gradually increased as the dynamic test progresses. In case of the A380, some early aircraft showed cracks at the wing root, so local reinforcements were added.
So the ugly truth is that cracks do occur regularly, but the structural design and the operating procedures ensure that they do not cause massive failures.

Thanks Peter ! It was a comprehensive explanation. I have, anyways seen the wings shiver in domestic civilian flights in Boeing 777 / A320 planes during take-off/landing

@saurabhsingh: The wings are very definitely designed to flex, in some cases quite a lot.  This is obvious if you look out the window during even light turbulence.


text:
What work besides flying planes does an airline pilot regularly do?
What are the typical non-aircraft duties for an airline pilot?
By non-aircraft, I'm asking about time spent in the office, in meetings, training (whether in a simulator, class or other non-aircraft environment), deadheading or being at the airport but not actually in the aircraft.
I understand there is paperwork and pre-flight planning done on the ground between flights while in the cockpit, so I'm not asking about this. I'm really trying to get an idea about what other work related activities you do which does not involve you being in the cockpit (except perhaps purely as a work-related passenger).
Another way of asking this question would be, "what work besides flying planes does an airline pilot normally do, or might reasonably be expected to do, as part of his or her job?"

Although the questions are different, but this answer explains several things which are needed in an answer for this question.

There isn't much non-flying duty for airline pilots.
The most important is recurrent training. Pilots are required to attend a refresher course at least annually. This school covers regulations, aircraft systems, and performance. The performance part involves computing weight and balance, airfield/weather restrictions, fuel required, etc (basically the same thing as a Cessna 172, but with much bigger numbers). Additionally, full flight simulators are used to teach and/or evaluate normal and non-normal (we don't get emergencies anymore) procedure. This training is usually concurrent with the groundschool.
Pilots are required to maintain their approach charts and aircraft manuals; changes come frequently.
A junior First Officer will spend an eternity (at least it seems like it) doing standby duty. This involves being available to take the place of any pilot who calls in sick or is otherwise unavailable.
All pilots must pass a flight physical. The implication is that they must maintain themselves in at least minimal health.
I hope this at least partially answers your question.

Just to add to this - these requirements (refresher courses, flight simulation evaluations etc.) are exactly the same regardless of the experience and seniority. I have a friend who is a Captain with Southwest Airlines here in the U.S. for the last 11 years, and was a First-Officer for the first 6 years. So, a total of 17 years and counting with the same airline and he is still required to attend everything on a regular basis.

@RaajTram there is some difference, e.g. if the airline isn't on a 9-month recurrent schedule for everyone then first officers get the sim once a year while captains get the sim every 6 months.  Captains are also subject to line checks annually.  The classroom groundschool (indoc, CRM, systems, etc) are the same for everyone.

I've been retired for 16 years, so I'm not at all up on what the current thinking is, but I'm really surprised by your statement that you don't get emergencies anymore. Does that mean you don't get such things as engine fires, engine out, emergency descents, loss of hydraulic pressure, etc. in simulator training now, or is it that these things are now considered simply non-normal as opposed to emergencies?

@Terry, I read that as "emergencies are now called 'non-normal', not emergencies", much like garbage men are now called "sanitation engineers". Of course, I might be wrong (but I hope not!).

They must also keep their manuals and navigation charts current, etc.

I think it depends on what kind of airline you are working for. If you are a pilot in a low-cost airline, preceding answers are precise. But for example, my wife is a pilot at Lufthansa, and they have their own engineering, own maintenance, repair & overhaul divisions etc., so they have a lot of "staff pilots" who spend about 50% of their time in the offices.
Examples are:

management pilots like fleet captains (the formal boss of the pilots of a specific a/c type)
technical pilot (writing procedures, discussing with manufacturers etc.)
project pilots (pilots with more background like IT or an MBA who can bring both worlds together)

The CEO of Lufthansa, Carsten Spohr, is a pilot himself, but do not think that he has any time to fly anymore.
I think most of the pilots like to fly, but some of them want to spend some time in the office either to be at home or to advance their careers.

Great insight! Thanks for the answer and welcome!


text:
Under 3rd Class Medical Reform, When Do I Need To See My Doctor?
Lets say I'm a 35 year old pilot who just had a medical renewed so that it doesn't expire until 2021. 3rd class medical reform (although not law yet) requires that I visit my regular physician once every 4 years.
When do I need to see my doctor?

Anytime prior to the expiration of my 3rd class medical?
Do I surrender my 3rd class medical and go to the doctor immediately (after regulations pass of course)?
Do I go to my doctor in 2020? 2019?
Do I wait until my 3rd class medical expires (or within a month or two)?
4 years after the expiration of my 3rd class medical?

And a bonus question:

Does the 4 year clock start ticking when my medical expires, when regulations are enacted, or some other time?

114th Congress Senate Bill 571 - Pilots Bill of Rights 2

AOPA has a good FAQ on this that has a lot of information, but since the FAA hasn't written the new regulations yet, no one really knows what the details will be.

The FAA hasn't written the regs yet so who knows. All that has happened is congress has told the FAA to write the refs
Personally I think it's foolish to use your personal doc. You're waving all your HIPPA rights and obligating your personal doc to report anything to the FAA without your consent.
-Robert

Law has been passed, the regulations need to be written, so the bill and terms are set out in the bill. Also the doctor doesn't report anything to the FAA, there is no FAA reporting and nothing I've read in the law obligates a doctor to report to the FAA, they would simply not sign off on your log book document.

By the way you should consider moving this "answer" to the comments, it really doesn't answer anything and is more of a commentary on the reform rather than addressing the specific question at hand.

The only law that was passed was a directive requiring the FAA to implement the regulation allowing it. The details the op is asking for have not been drafted yet.

I’ve heard people say that they wouldn’t use their personal physician to do an FAA medical but it never made sense to me. If your personal physician finds something that disqualifies you from flying, then by definition you are breaking the regs if you fly. On the other hand, if your personal physician is also your FAA medical examiner, then they can make sure you aren’t taking any meds that are prohibited by the FAA, alert you to any conditions that, if left untreated will cause problems on your next medical, and in general be better equipped to keep you in the air.

Personal physicians in general know nothing about FAA rules so there is no such possibility of a personal physician finding something that disqualifies you from flying unless that physician is also an AME. What was proposed is no different than the LSA rules where you self-certify in combination with your physicians medical recommendations.

A personal physician may find everything to be disqualifying.


text:
What is a typical working day like for an Australian airline pilot?
What is it like working for a domestic airline in Australia (e.g. Virgin, Regional Express, etc)?
Obviously we're all here because we're interested in flying, but as for the practical aspects of being employed in the airline industry I'm trying to get an idea of some of the following:

What does a typical working day look like and what are the hours?
What are airlines like as employers?
What is the best thing (or things) about your job?
What is the worst thing (or things) about your job?

Thanks!

This is a very open-ended question as airlines' jobs vary greatly from country to country, and what is true for one country would be very different in another.

@Farhan I've narrowed the scope of the question to Australia.

Somewhat similar to this question: http://aviation.stackexchange.com/questions/8456/burdens-of-working-as-an-airline-pilot

Australia? Wake up, try not to get eaten by a snake. Get dressed, try not to be bitten by a spider. Go out to the car, dodge a crocodile...... Etc

@JonStory You forgot to dodge the dropbear, feed the bunyip and ride the kangaroo to work.

Can somebody please ask What is the typical working day of a Russian pilot? so I can say "not to be confused with ..."

I'm surprised no-one chose to answer this. I think it's a useful question. So what if it's opinion based, that's the point of getting a few different answers. @usernumber - thanks for linking that other question, it's the one useful response to my question.

@MarkyMark It's not "so what" that it's opinion-based. Stack Exchange's system of supposedly objective voting on answers falls apart once the answers cannot be judged objectively. How is one answer to "what is the best thing(s) about your job?" more correct than another? On what criteria do you select a "best" or "most useful" answer to accept?

The question is a bit open-ended, but a typical day for a domestic short-haul pilot on one-day trips might be 2 x 4.5 hr transcon sectors or  2 x return east coast 1.5 hr sectors (6 hours stick time). For multi-day trips, the average stick time might be about 5 hrs each day. It really depends on the patterns. What are airlines like as employers? The answer depends on your own point of view, but in general, things are highly professional ( for both employer and employee), compared to many other places. Safety is a big deal in Australia - both employer and employee take it very seriously.


text:
Determining total engine life in relation to SMOH/SFOH
When evaluating the value of an aircraft, the total hours since major (or factory) overhaul (SFOH/SMOH) is an important indicator of price since it tells us how many hours the engine has operated since the last overhaul.
I read in another answer that the typical time between overhaul (TBO) interval for a piston engine is 2000 hours.
However, what is the best way to determine the actual TBO interval for a given engine model? I'm hoping someone might know of a handy list somewhere rather than having to dredge through service manuals for each model I'm interested in.

2000 is common but that depends on the engine. The official TBO is what ever the TC/manufacture states, here is the list for of the Lycomings published by Lycoming and here is the continental list. These are manufacturer recommended TBO's and are presumably based on data and tests they have run but they are in the end an estimate and usually reflect a relatively cautious value.
The "actual" TBO is a somewhat subjective number that no one can give you. Internet data and general collaboration can help you get a picture of what to expect for a given airframe/engine combination but individual units must be handled on a case by case basis. When assessing any aircraft its good to look for statements like "generally makes it to TBO" or "this aircraft had a lot of engine issues" or "oh man that turbo charger made that a finicky power plant" then come to your own conclusion. Forums, message boards, and old APOA articles can be your friend on these matters. Oil analysis and compression testing is the best objective way to measure engine health and a good pre-buy is important for that. Some people say "if it ain't makin' metal keep on flying it"

I used to know an overhaul mechanic who said that Lycs will easily run 3000 hrs+ although they typically require line boring if run that long.  Anyway, the other really big issue on a pre-buy is to review the logs for periods of long inactivity.  In Canada aircraft have to have journey logs so it's easy.  Not sure how that works in the US.

Great point.  Engines that run regularly live long happy lives.  Engines that sit...not so much.

TSMOH alone doesn't tell you much.  The condition is what matters.  There are many examples of brand new engines failing within the first 100hrs and many more examples of decently maintained engines ticking along well past 3000hrs.  150hp mogas O-320s I flew as a CFI racked up ~3500 hrs in some cases and may or may not have had a dash of MMO here and there...who's to say?  In fact, a low time engine is much more likely to fail than a high time example if the same engine (I'll search for the backup to this claim and post it here if I remember).  Give me a 2000hr O-470 over a 10hr O-470 any day of the week!
TBOs for most horizontally opposed engines range from a low of 1200hrs on some of the older geared engines to a high of 2400hrs.  The calander limit is generally 12yrs but nobody ever talks about that.  TBO is not really a good indicator of engine life, though.  In the US, we run "on condition" meaning that the TBO is merely a reference, not a limiter.  If the engine is healthy and is not giving you any bad signs then there really is no reason to drop ~$30,000 or whatever on an overhaul.
Each manufacturer has a list of their hour and calendar TBOs but, again, they don't mean much to a part 91 owner/operator.  Certain commercial operations must adhere to the hour and calender TBOs but even then the FAA will grant extension waivers in many cases.
Personally, I would not hesitate to buy a plane with an engine at or near TBO...after a thorough inspection, of course.  I'm confident I can get another few hundred hours out of a healthy engine.  And if I don't...fine.  I priced the engine as a runout and will drop a mid-time engine in sourced from someone doing an engine upgrade!
Published TBOs for common piston engines:
TCM - http://www.continentalmotors.aero/uploadedFiles/Content/xImages/TBO%20Page%20SIL98-9C.pdf
Lyc - https://www.lycoming.com/sites/default/files/SI1009BD%20TBO%20Schedule.pdf

Would you please define MMO?

Marvel Mystery Oil. Some people swear by it, others say it's useless. You'll need to determine if it is legal to use in certified aircraft.  I've heard arguments both ways.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Why are the exhaust pipes design on the Ilyushin Il-2 not very popular?
This is a piece of this image from Wikipedia

Note the circled region. Movies often show exhaust fumes coming from those pipes when the engine is started. So I assume these are actual exhaust pipes.
This design doesn't appear very often, especially in modern piston engine airplanes. Why is this the case?

I think a lot of it has to do with noise. This design was popular on propeller driven fighter (military) aircraft that didn't care about noise.

also, this aircraft has a V12 engine ( https://en.wikipedia.org/wiki/Mikulin_AM-38 ) like the Merlin in the Spitfire, so the layout makes sense. with radial engines and flat opposed engines, this type of exhaust configuration wouldn't make sense

Compare to other aircraft of the same period, I think you'll find it very common indeed.

It was popular at that time. All the Curtiss P-40 Warhawk, North American P-51 Mustang, Hawker Hurricane, Supermarine Spitfire, Hawker Tempest, Messerschmitt Bf109 and many more had similar.
That kind of exhaust was tied to the engine, a water-cooled 2-line 12-cylinder (V-12) and later some 4-line 24-cylinder (H-24 or X-24) engines. So there was a row of cylinders on each side and each had its own exhaust pipe as short as possible to minimize its resistance.
Since then, anything with more than 6 cylinders was replaced by turbines and all the smaller engines are air-cooled, because in GA aircraft the simplicity of air-cooled engine is more useful than the slightly lower drag of water-cooled one (navy preferred air-cooled even in fighters for the same reason). And air-cooled engines generally have their exhaust pipes lead into the cooling air stream and thus hidden under the cowling.

Basically anything with a V-12 had more or less that setup. Anything with a Merlin or other RR engine, all the Allison and Packard V-12s in the US, all the V-12s in Soviet and German fighters... the list goes on. Pick a V-12 engined fighter from WW2 and you'll see this exhaust style.

@egid, what surprises me is that there didn't seem to be any V-10, V-14, V-16 and other sizes. It was all V-12 and later some H-24. They exist in other domains, but not in aviation.

@egid, Mosquito seems like a notable exception with the exhaust covered by some kind of common cowling.

Not in photos I've seen? Maybe the inboard pilot's side has a flash hider or something... example

@egid, many of the pictures on WP have it. Not all though.

Yeah, maybe related to nighttime bombing use? They used Mosquitos as pathfinders, perhaps they wanted to minimize warning at low altitude?

@egid, probably. After all, in a sense it was the first stealth aircraft.

I believe they were called flame dampers.  Exhaust flames were visible at night.

I only see five pipes, not six.

@sharptooth, This picture shows there are 6, but the last one is more straight and very close to the fifth, so they can't be distinguished from the angle the image you posted was made from.

This engine is about 10 times more powerful than a modern average piston engine. With such power you get some useful thrust from exhaust power directly. This design helps to recover it. With a small SEP, noise and keeping exhaust smoke away from the cabin probably is more important. And it's not true that it's not popular. It's popular with single engine turbines. Source: Wikimedia (click for link)

Or multi-engine turbines, for that matter.

I don't actually think there was much thrust to extract. The key point was not creating resistance inside the exhaust pipes themselves.


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What is qualitative relationship between surge line, stage characteristic and throttle characteristic?
I have referred to standard author books and online tutorials but I am still quite confused about how the Stall and Throttle characteristics lead to Surge.
1. Why and how does the throttle characteristic affect the compressor performance because as far as i know, the next consecutive element in an engine after a Compressor is a Combustor, and the throttle comes at last,after combustor and turbine,  assuming throttle is same as nozzle (if not please correct me).
Assume i am talking about turbojet engines and Axial compressor, just to have a picture in mind.
2. How does the throttle characteristic curves come out to be like that?
And why does the mass flow decrease when we throttle the compressor?
3. I am also unable to grasp the concept which causes the evil fluctuations in the flow during surge, which leads to reverse flow and damage of the components.

Source:- Hill Peterson- Thermodynamics of Propulsion.
Someone please explain the concepts as much as possible.

The throttle adjusts the fuel flow, much like the gas pedal does in a car. And: Between the compressor and the combustion chamber is a diffusor which wants to be treated properly to avoid flow separation.

Just FYI, the throttle on a car is called that because on a carbureted engine it would restrict (or throttle) the airflow going into the engine, not the fuel directly.

Since your question is divided in three parts, I do the same with my answer. First, however, we need to explain what the axes of the graph mean. The x-axis plots mass flow through the compressor, which is roughly equivalent to the tip speed of the compressor blades, and the y-axis shows the pressure ratio between entry and exit flow.
Throttle and compressor performance
The throttle regulates fuel flow, and this flow has to match the air flow. The limits are:

If fuel flow is too high: The combustion will create too much heat, so the turbine will be damaged.
If fuel flow is too low: Too little energy is added to sustain the current operating point. The engine will slow down.

If it is kept within those limits, the throttle will indirectly control the compressor speed and it's mass flow. More fuel flow will translate into higher turbine entry speeds, which will increase the torque produced by the turbine and speed it up. Since it is directly coupled with the compressor, it will see the same speed increase. This leads to higher mass flow and a lower fuel-to-air ratio in the combustor (relative to the state right after the throttle increase), such that a new equilibrium at a higher speed is established.
Throttle lines
For every pressure ratio the compressor will have a matching mass flow, and both move up and down in parallel. This is shown by the dashed lines. Depending on the blockage of flow in the turbine and the engine nozzle, different lines are shown for different grades of blockage. The solid stage characteristic line shows the limits within which the compressor will run, and a higher flow resistance narrows the range of speeds that are possible. The limits are determined by:

Lower limit: Here the compressor is run at the lowest possible speed for the given blockage, and the compressor blades run close to their maximum lift coefficient. When the blockage is increased, the flow over the compressor blades will stall and the pressure ratio will collapse.
Upper limit: Here the compressor blades run at high speed and a low lift coefficient. Running them any faster will not create enough pressure rise per stage, and again the blocking cannot be overcome.

Surge
Once the pressure rise per stage cannot be maintained (say, due to a stall of the flow over the compressor vanes), the high pressure air in the combustor will find it easier to escape at the front than to flow through the turbine and the nozzle. This leads to reverse flow and a sudden drop in combustor pressure, which in turn allows the compressor to reverse the flow and start pumping air back again. Now the pressure in the combustor rises again, until the whole process repeats.

Doubt:- 1. So throttle is used to regulate mass of fuel, fine. But then acc. to u, when we increase fuel mass, it should logically increase air mass flow also, but how can you say that it would lead to a LOWER fuel to air ratio directly, when both of them are increasing. Is their any mathematical, empirical or logical reason to explain that?

Can you please elaborate a bit on the surge part, where on the right side of E we have a stable flow and on the left we have an unstable flow. Because both the sides the pressure ratio decreases, so why is it so that reverse flow effects only while reducing the mass flow beyond E.(even slightly).

@Manish: 1. When you increase the throttle, the fuel-to-air ratio gets richer. Then, as turbine power and mass flow go up, it becomes leaner again. It is lower in relation to the state right after the throttle change. 2. On the left side of E blockage is too high, so no stable point exists. Mass flow equals tip speed, and at the lower speeds the possible pressure ratio is too low to allow the engine to operate.


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What is the function of the lower vertical fin on a MIG-23?
I would like to ask about the function of the lower vertical fin in Mig 23 .

Maybe it's to let Russian pilots know when they're flying too low.

note that other aircraft such as the F-16 has the same feature.

Directional stability at supersonic speed.
The air above the aircraft is less dense at supersonic speed, and elasticity reduces the effectivity of the fin - it bends and twists from the air loads. Conversely, the lower fin operates in denser air and creates more side force per area.
Also, the lower fin shifts the aerodynamic center of the empennage downwards, which is improving the handling characteristics. Adding area below the centerline helps to reduce the roll contribution of the vertical tail in a sideslip, which improves handling characteristics (more directional stability AND lower yaw-induced roll).
As long as the vertical tail surface sits above the centerline (more precisely the longitudinal axis of inertia - for now we can assume both fall together), any side force will also create a rolling moment.  This is undesirable because now a yaw command will not only create the intended yawing moment, but also a rolling moment.
If you want to yaw in order to turn, the vertical tail above the centerline will even roll the aircraft in the wrong direction, so you need more coordinated aileron command than with a symmetrical vertical tail.
The MiG-23 is not alone: Many supersonic combat aircraft use ventral fins. See the picture below for an example where the effects of additional vertical tail area are compared to the effects of a ventral fin of the same area.

(Source: Ray Whitford: Fundamentals of fighter design)
At supersonic speeds, the stiff, low aspect ratio ventral fin has a nearly constant contribution to directional stability, whereas the wing-like vertical tail loses effectivity in proportion to the Prandtl-Glauert factor $\frac{1}{\sqrt{Ma^2-1}}$ because it bends and twists more due to its higher aspect ratio. The small ventral fin of the F-104 raised directional stability by 30% at Mach 2.

(Source: Ray Whitford: Fundamentals of fighter design)
At high angles of attack, the vertical tail is in the wake of the fuselage which reduces local dynamic pressure and, consequently, effectivity. The ventral fin then is in ideal flow conditions, so it can help to stabilize the aircraft at high angle of attack, just when the fuselage contribution to instability is largest.

It is called called a ventral fin and is used to provide improved stability. A number of combat aircraft (like F-14, F-8, for example) have them. the image below shows the ventral fin in F-8.

Image from nasa.gov
Adding a ventral fin helps in increasing directional stability (especially at supersonic speeds) and reduces yaw induced roll (as the roll contribution of vertical fin is reduced in a sideslip). This improves the handling qualities. Another advantage is that they retain their effectiveness at high angles of attack, while the vertical fin may be blanked by the main wing.
The ventral fins in Mig 23 were quite big, which necessiated folding them when landing.

MiG-23 with wing flaps lowered, landing gear deployed, and ventral fin folded aside as it approaches to land; image from aerospaceweb.org
This is not limited to Mig-23; Vought XF8U-3 'Super Crusader' also had quite large ventral fins, which required folding.

That piece of tail under the belly made it easier for the MiG-23 to be stabilised in high speed conditions. That part would be folded away for ground operations if you are also curious about that.
Source

authors: เด็กชายชนะพล รูปงาม


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Is the aircraft neutral point a function of the tail incidence angle?
While using XFLR v5 for a basic analysis I am facing this issue. For a fixed configuration I varied the tail incidence angle and XFLR is displaying a change in the Neutral point location. But as per theory neutral point location is not dependent on the tail incidence angle at all. I was hoping if someone could help me with this issue.

As you suggested, neutral point does not change with changes in decalage (tail incidence).
For more explanation, see these links from a model airplane forum--
https://www.rcgroups.com/forums/showpost.php?p=24692807&postcount=3
https://www.rcgroups.com/forums/showpost.php?p=24694083&postcount=7
https://www.rcgroups.com/forums/showpost.php?p=24694082&postcount=6
https://www.rcgroups.com/forums/showpost.php?p=24694515&postcount=9
The links are more focussed on "static margin" than "neutral point", but implicit in the idea that the "static margin" is not changing if the decalage is changed, is the idea that the "neutral point" is not changing either.
Maybe someone can add to this answer to address the issue you are having with XFLR v5.

I have done some homework and I will explain why the Neutral point does not vary with the tail incidence angle.

The above equation is the fundamental equation defining the location of the neutral point.
We can see that the Neutral point is a function of the following factors only,

Aerodynamic centre
Tail volume (Horizontal tail sizing and Arm length)
Tail efficiency factor (Ratio of dynamic pressure at the tail and at the wing),
Lift curve slope for the wing and HT (CLalpha - which is fixed and not dependent on the tail incidence),
Downwash effect
Fuselage moment contribution

So none of these factors are dependent on the tail incidence angle and hence there musnt be a change at all. What shocked me the most is the fact that errors in variable quantites can be accounted for but errors in quantities that shouldnt vary is very confusing. It is a very standard statement that '' Static margin or ultimately the Cmalpha shouldnt get affected by the change in tail incidence''
This is the information I could get about it.

The calculation of the neutral point of an aircraft is about moments, not aerodynamics. The tail incidence angle has nothing to do with the neutral point, just as it also has nothing to do with the calculation of the CG.

But moments arise because of aerodynamics! Stability is about reaction to disturbances; with most disturbances, airflow changes, which leads to change of moments, which provide that reaction. You can't separate them.

The above answer is correct.  In the past I've seen a very clear explanation of this on model airplane forum.  I will add a link to that discussion when I come across it.

@Zeus CG does not take into consideration anything but weights and arms while the aircraft is not in motion. Neutral point is a measurement relative to the CG for the purposes of determining positive or negative stability. That is why you do not take into consideration those things you mentioned.

You said "calculation...  is about moments, not aerodynamics". This is "not even wrong": most moments are aerodynamic. That's what I was referring to.

@zeus You still don't understand. CG and neutral point calculations are static calculations. No "dynamics.' Have you ever actually done a CG or neutral point calculation? Here, this explains both in very simple terms. Notice the diagrams: angle of incidence is not present in any of the explanations. https://www.instructables.com/id/Introduction-65/

I have. The 'dynamics' in 'aerodynamics' refers to the moving airflow, nothing more. Not to the dynamics of the aircraft. In static conditions you can consider static moments, but they (except for gravity) are still called 'aerodynamic'. It's just this simple terminology I'm pointing to. Everything about flying (heavier-than-air) craft is aerodynamics.

I'm not that familiar with XFLR, so I'll answer with the general knowledge.
The neutral point (aka aerodynamic centre, AC) does change with the tail incidence. Why shouldn't it?
The peculiarity (and intention) of AC is that it doesn't move with the angle of attack (AoA) only. If you balance your airplane at AC, by locating CG there or by hinging (and weight balancing) the model in a wind tunnel, the airplane will be neutral with respect to AoA changes. It won't 'weathervane'.
But this doesn't mean AC won't move with configuration. If you pull the elevator/stab up, this will redistribute the moments such that the neutral point moved farther back. Think this way: AC, by definition, is the point about which the added moments due to increase of AoA from the wing, stab and everything else, balance each other out. Or, in other words, where we can think the added lift occurs. When you reduce the stab incidence (with respect to the wing), you make it to contribute more to the moment balance (again, the balance due to changes of AoA and nothing else, it's boring to repeat but it's important to understand. We are not talking about the absolute balance).
But what can you do with that? Your stab now produces a pitch-up moment. Yes, the airplane actually became a bit more stable, but it will start doing loops. If we want to restore neutrality, we'd need to move CG back, to the new AC - which would only make things worse. The only way we can balance the situation(*) is to move CG forward, until it compensates the added pitch-up. Which again increases static stability. (In practice, of course, the opposite happens: when CG is forward, we make the tail to provide pitch-up).
So, in reality, we can't simply choose tail incidence as an independent variable. It is needed to trim the airplane as much as to provide stability. But, indeed, any aerodynamic configuration changes may shift the AC and affect stability.

(*) We can also tilt the thrust to provide the required moment, but this would be double waste: the tail works against the engine. Nevertheless, technically, this way it is possible to make a statically neutral airplane with any desired tail incidence.

Why shouldn't it? Because as long as the lift is proportional to angle of attack (almost correct unless approaching stall) and the centre of pressure of each airfoil (wing and stabiliser) does not move with angle of attack (slightly incorrect), the same change in angle of attack will cause the same increase in force at the same two points independent of how you shift the zero lift line, and consequently the neutral point around which there is no moment will be the same. In practice the centres of pressure do move a little, so there is slight variation.

@RobertDiGiovanni, Neutral point is not center of all lifts! That would be overall centre of pressure. Neutral point is a point around which the pitching moment does not change with angle of attack (a.k.a aerodynamic centre; neutral point is usually used of the whole aircraft, aerodynamic centre of individual airfoils). In all practical aircraft, the neutral point is significantly behind the overall centre of pressure, which must coincide with centre of gravity in straight flight.

This may be a good time to dig into the formulas your software uses and try doing them manually.
It seems XFLR v5 is doing a few steps at a time.  Changing tail incidence indirectly affects the static stability nuetral point by assuming CG will move to new center (of lift) pressure.
Moving CG changes the torque arms of the stabilizing and destabilizing forces, which will change the static stability of the aircraft.
For example, is one reduces downforce of tail, center of pressure (of entire plane) moves back, matching CG moves back, now there is more area ahead of the CG.  One cannot ignore the CG when considering the effects of aerodynamic forces on an aircraft.
If one defines "nuetral point"  as the aerodynamic center of the entire aircraft, where a change in pitch does not create a pitching moment, then a change in tail incidence should only slightly affect its location.  This net aerodynamic center still needs to be behind the center of gravity for positive stability.
More good info in this answer.


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In the US, is it customary to tip the line personnel?
The etiquette of interacting with the line personnel wasn't really taught to me during flight training, and I feel that every time I ask for line service, I'm doing something wrong by not tipping. I don't travel with groups or other pilots very often, so I don't see this in practice...
Do line workers in the United States expect tips for service (fuel/parking) from GA pilots?

There are a lot of discussions in various forums about this, and lots of opinions. The general consensus seems to be that it's not expected for basic fuel/parking service, but cleaning, carrying bags, driving you somewhere etc. definitely deserves a tip. But plenty of people tip for all service, just because they can or to support the FBO in some way. I once locked myself out of a C172 and a tall, thin line guy opened the baggage door and somehow contorted his upper body in far enough to open the pilot's door by using a towbar to pull the locking lever. That was well worth 20 bucks!

You don't have self-service avgas where you fly?

I've never tipped for aircraft refuelling or other line services, and have never been criticized or looked at the wrong way for not doing so. That said, tipping in the US has nothing to do with the industry in which the person works; it's a personal reward for good service, and it is both appreciated as well as remembered the next time you are there.

FWIW, I'd say the industry is definitely relevant. 15-18% is expected as standard for restaurant service, for example, but not necessarily in other situations.

In some countries tipping is considered an insult. That's happened to me in Japan when I tried to tip an older taxi driver. Learned my lesson -real- quick. :)

BTW, the biggest difference between the restaurant and FBO services when it comes to tipping is that people in restaurants have come to expect tips regardless of the quality of service. I have been known to walk right out of a restaurant that says its policy is to add x% to the bill automatically for tipping. I do not tip automatically, ever, and if a restaurant ever tries to add a tip to a bill without my consent I scratch it out and revise the total to what I think appropriate. If they still try to charge me the tip, I dispute the bill and the restaurant always loses.

That 'expectation' is so deeply ingrained in the US that the government allows businesses to pay below minimum wage to tipped staff because it's assumed that tips will make up the difference. You can disagree with that policy if you like, and only eat in states or restaurants that pay full federal minimum wage, but it's not very realistic. To keep this aviation-related, automatically adding tips to the bill seems especially common in airports, because foreigners don't know the background and 'short' the staff by not tipping.

The reason for the policy is to encourage service staff to do what they are supposed to do, provide good service. Not tipping for bad service is not "shorting."


text:
How can I correct the heading for this navigation problem?
I'm a pilot trainee in Hungary and just encountered a navigation question problem which is from the PPL Training Questions book. Would be glad if someone can briefly explain how to do this typical question which I come across a lot.

An aeroplane has a heading of 090°. The distance which has to be flown
    is 90 NM. After 45 NM the aeroplane is 4.5 NM north of the planned
    flight path. What is the corrected heading to reach the arrival
    aerodrome directly?

a) 6° to the right,
b) 9° to the right,
c) 18° to the right
d) 12° to the right

You must understand the "1 in 60 rule". It will be in your exams and is very useful if you are flying without a GPS.

Not familiar with the aviation way, but geometrically:
After 45 NM, wind pushed you 4.5 NM aside. Over the next 45 NM, you need to be 9 NM to the other side. (4.5 to compensate the side  wind to come, 4.5 to go back over what you already lost).
Arctangent of 9/45 is quite close to 12 degrees.
This only holds if the perpendicular component is negligible (at 1/10 it is).

The correct answer is 12 degrees.  The problem is as follows:

To determine wind correction use an E6-b or similar.
Set distance off course over distance already flown.  In this case, $\frac{4.5}{45}$. The degrees to eliminate wind drift will be under the rate arrow, in this case: 6.
Then, determine how much additional correction is needed to rejoin.  In this case, $\frac{4.5}{45}$ again.  You must add 6 more degrees to the first 6 to rejoin.
The total (therefore the answer) is 12.

your answer is excellent, but we may wish to clarify "heading" as the direction the nose and directional indicator (little airplane on instrument panel) is pointing.  With cross wind, "heading" of 090 will produce ground track of 084.  The pilot must "point" 096 to aim at destination plus 6 degrees to the right (102) to track in that direction.  Little nitpick, your thoughts on this are appreciated. +1

It's a good comment especially in this day and age where handheld GPS users are used to seeing "heading" used to indicate the direction of ground track if the device has no internal compass.

I did arc sin 4.5/45 and 6 degrees to the right was the closest answer.  This is assuming no cross wind, just navigational drift.  Arc sin was made from a triangle of 4.5 to correct and remaining distance of around 45 NM.
However, you may ask to specify whether or not this is a cross wind issue.  If it is, the effect of wind on the remaining track would have to be calculated from the point you were at and the new heading to your destination.
If the cause of the drift was unknown, 12 degrees right would also make sense.
But in real life this is where you would start looking for landmarks such as roads, terrain,
lakes etc. to help find your destination.
EDIT:  correction without wind:  point nose to 096 degrees (this is the direction to your
           destination)
           correction with wind: point nose to 102 degrees
We can see how this is a confusing question, as the CORRECTION in both cases is 6 degrees to the right.   Because it is highly doubtful anyone would fly 084 the whole time before noticing the error, the most probable cause is wind drift. The correction is 12 degrees right from ORIGINAL heading and/or 6 degrees right from the NEW heading.
Even if I got this "wrong" on a test, it would be something remembered and learned from.

This is why it is a good idea to have checkpoints along the way to stay on course.

In the aviation context I think there is a presumption here that the deviation was caused by a wind which is assumed to continue for the rest of the flight, but you do have point.


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How do I answer this navigation problem?
This question is from the PPL questions book, navigation part.

Given: QDM: 279° VAR: 5° W DEV: 5° E
  The QDR equals...

What have you tried so far? Is there are specific part you don't understand?

Correct me If I'm wrong. I know that the DEV part is used to get the Magnetic Heading and what I should do is subtract 5 degrees from the given QDM but what should I do with VAR which is given. Is that about the Course Heading? Confused.

QDM is magnetic bearing to station, QDR is magnetic bearing from station so VAR and DEV are here only to confuse you; the QDR is opposite of QDM so the answer is 099.
Notice that QDR and QDM do not depend on aircraft’s heading or flight path, they are only dependent on A/Cs location relative to the station.


text:
Is the Inspire 1 a good drone starter aircraft?
First of all, I'm not totally positive that this will be well received here; I did read the related meta, but am unsure. I have also asked the question in support of the new Drone SE.
I'm new to drones, and I've been researching. Would it be a bad idea to start out as a beginner with the Inspire 1 (sort of the cutting edge, top of the line, nicest looking drone out there)?
I read somewhere that with Drones, unlike normal RC aircraft, (and large aircraft perhaps) the higher the price, the easier the flying. I'm worried about whether or not getting a very high end drone as my first one might prove a foolish investment?

I'm not sure this question will remain open long but here's my $0.02:

You will definitely want to learn to fly a cheap quadcopter before going expensive. Quadcopters are not that easy to fly (there is a lot going on at the same time: 6 degrees of freedom being controlled in a changing frame of reference depending on orientation to a stationary pilot).
I crashed my cheap one a lot learning to fly it despite it being pretty stable, but it is robust and takes a good beating. A cheap one is a very low risk and pain compared to the one you're looking at: You're not going have to break a lot on the expensive one to recoup the investment of becoming acquainted to quadcopters before you started.
Quadcopters may become a little 'smarter' as you go more expensive and be more stable, but it still requires good piloting.